1. Field of the Invention
The present invention relates to an apparatus and method for configuration and optimization of an Automatic Neighbor Relation (ANR) in a wireless communication system. More particularly, the present invention relates to an apparatus and method for automatically recognizing inter-Radio Access Technologies (RAT)/frequency cells and for identifying and managing the inter-RAT/frequency cells according to a handover purpose (i.e., mobility guarantee and load balancing/cell outage compensation) in a wireless communication system.
2. Description of the Related Art
A 2nd generation (2G) mobile communication technique generally provides voice-oriented services and includes Global System for Mobile Communications (GSM), Interim Standard (IS)-95, etc. GSM was commercialized in 1992 in and around Europe, and provides a service by using Time Division Multiple Access (TDMA). IS-95 was commercialized in and around Korea and the USA, and uses Code Division Multiple Access (CDMA).
A 3rd generation (3G) mobile communication technique, evolved from the 2G mobile communication technique, refers to a mobile communication technique supporting not only a voice service but also a packet service, and uses CDMA. The 3G mobile communication technique includes 3rd Generation Project Partnership (3GPP) or Universal Mobile Telecommunication System (UMTS) as European and Japanese standards based on asynchronization between Base Stations (BSs) and 3rd Generation Project Partnership 2 (3GPP2) or CDMA2000 as a USA standard based on synchronization between BSs. The 3GPP proposes Frequency Division Duplexing (FDD) for dividing uplink/downlink communication in terms of frequency and Time Division Duplexing (TDD) for dividing uplink/downlink communication in terms of time in order to improve efficiency of limited channel usage. The use of TDD includes Wide-Band TDD (WB-TDD) using a chip rate of a 3.84 Mega chip per second (Mcps) and Narrow-Band TDD (NB-TDD) using a chip rate of 1.28 Mcps.
When a service based on the 3G mobile communication technique is commercialized, it is apparent that this service will coexist with a service based on the 2G mobile communication technique which has already been commercialized and is presently in use. In this case, the 2G and 3G mobile communication systems use different frequencies or communication schemes and thus a method for providing mutual compatibility between the two systems is required. In particular, a handover-related issue is the most urgent issue to be dealt with in order to provide mutual compatibility between the systems using the different communication schemes or the different frequencies. That is, systems which use different communication schemes (e.g., FDD, WB-TDD, NB-TDD, GSM, CDMA2000, etc.) as described above or which use the same communication scheme but use different frequencies may exist consecutively across several regions. In such a situation, if a User Equipment (UE) moves from the coverage of a BS which currently provides a service by using a specific communication scheme and a specific frequency to the coverage of another BS using another communication scheme and/or another frequency, a handover is necessary between the BSs for global roaming. In this case, the handover between the BSs includes an inter-frequency handover and an Inter-Radio Access Technologies (RAT) handover.
The inter-RAT handover is a handover between mobile communication systems using different communication schemes. For the inter-RAT handover, a UE is required to monitor a state of a BS as a target of the handover (hereinafter, referred to as a target BS) in a mobile communication system. The monitoring of the target BS is referred to as “inter-RAT measurement”.
The inter-frequency handover is a handover between mobile communication systems using different frequencies. That is, the inter-frequency handover implies a handover used even when BSs of mobile communication systems using the same communication scheme use different frequencies. For the inter-frequency handover, the UE also has to be capable of monitoring the state of the target BS. The monitoring of the state of the target BS is referred to as “inter-frequency measurement”.
A method for configuration and optimization of an Automatic Neighbor Relation (ANR) is used in a Self-Organizing Network (SON). At present, a Neighbor Cell List (NCL) is manually created through coverage predictions by using a cell planning tool before the BS is installed. However, it is difficult to obtain the NCL correctly due to an imperfect map and building data, and thus a drive/walk test is additionally performed to obtain a correct NCL. The NCL created through the coverage predictions is used directly without alteration. However, a new cell may be added near an area where the BS is currently being operating, or the existing cell may be removed. In addition, due to an environmental change, the coverage of the existing neighbor cell may change and thus a Neighbor Relation (NR) may change. Therefore, when the NCL does not change, a handover may be made to an unsuitable cell. Further, a handover delay may result in an increase of a call drop rate and a decrease of system performance. Accordingly, there is a need for a new method for automatically maintaining an optimal NCL depending on the environmental change.
The conventional method for configuration and optimization of the ANR primarily relates to an intra-frequency Long Term Evolution (LTE) network. A cell deployment type was hot-spot deployment when the LTE was first introduced and soon will extend to one-to-one deployment. As a result, an inter-RAT/frequency handover may frequently occur. Therefore, for service/call continuity, there is a need for a method for configuration and optimization of a Neighbor Relation Table (NRT) by automatically recognizing a cell for the inter-RAT handover (hereinafter, ‘inter-RAT cell’) and a cell for the inter-frequency handover (hereinafter, ‘inter-frequency cell’).
The inter-RAT/frequency cell is deployed for the purpose of capacity improvement. For this, the deployment type includes 3 types, i.e., hot-spot deployment, one-to-one deployment, and disjoint deployment.
FIGS. 1A, 1B and 1C are diagrams for illustrating a deployment type of an inter-Radio Access Technologies (RAT)/frequency cell in a conventional wireless communication system.
In the case of hot-spot deployment, as illustrated in FIG. 1A, cells 100-1 to 100-4 having one RAT/frequency (e.g., RAT1/F1) are basically deployed, and cells 101-1 and 101-2 having another RAT/frequency (e.g., RAT2/F2) are additionally deployed in a hot-spot area. Mobility guarantee is the most important issue in the case of using hot-spot deployment. Service/call continuity must be guaranteed for UEs located in the edge of the cells 101-1 and 101-2, and for this, the cells 101-1 and 101-2 must manage the cells 100-1 to 100-4 as neighbor cells. Of course, in addition to the mobility guarantee, load balancing may also be a HandOver (HO) scenario in hot-spot deployment. However, since the mobility guarantee is the primary purpose, in the case of hot-spot deployment, a handover is performed by selecting inter-RAT/frequency cells suitable for the mobility guarantee.
In the case of one-to-one deployment, as illustrated in FIG. 1B, cells 102-1 to 102-4 having one RAT/frequency (e.g., RAT1/F1) are basically deployed, and cells 103-1 to 103-4 having another RAT/frequency (e.g., RAT2/F2) are respectively overlaid with the cells 102-1 to 102-4. In the case of using one-to-one deployment, a relation between one RAT/frequency and another RAT/frequency is more significant in terms of load balancing between the two in comparison with the mobility guarantee. This is because, since a Radio Frequency (RF) condition from a cell corresponding to each RAT/frequency to a UE is similar when fully overlaid, signal quality recognized by the UE from the cell corresponding to each RAT/frequency is also similar, and thus a probability of handover occurrence for the mobility guarantee is relatively small. The inter-RAT handover is a compensation method used when cell outage occurs. Therefore, in the case of using one-to-one deployment, there is a need to identify overlaid neighbor cells and to manage the identified overlaid neighbor cells by using an NCL useful for load balancing or cell outage compensation.
In the case of disjoint deployment, as illustrated in FIG. 1C, cells 104-1 and 104-2 having one RAT/frequency (e.g., RAT1/F1) and cells 105-1 and 105-2 having another RAT/frequency (e.g., RAT2/F2) are deployed without being overlaid. UEs located between the cell 104-2 having the RAT1/F1 and the cell 105-1 having the RAT2/F2 in FIG. 1C always require a handover for service/call continuity. In the case of using disjoint deployment, the inter-RAT/frequency handover puts a higher priority on mobility guarantee than load balancing. Therefore, there is a need to select neighbor cells suitable for mobility guarantee and to manage the selected neighbor cells by using the NCL for mobility guarantee.
As such, the purpose of using the inter-RAT/frequency handover varies depending on the deployment type of inter-RAT/frequency cells, unlike the intra-RAT/frequency handover. This is because the intra-RAT/frequency handover is used primarily for the purpose of mobility guarantee, whereas when using the inter-RAT/frequency handover, cells each having a different RAT/frequency may cover a similar area according to the deployment type of the inter-RAT/frequency cells. Therefore, there is a need for a method of identifying a neighbor cell that may be used for the purpose of load balancing/cell outage compensation or the like in addition to mobility guarantee. That is, there is a need for a method of recognizing a deployment type of inter-RAT/frequency cells and of identifying and managing the inter-RAT/frequency cells according to a handover purpose (i.e., mobility guarantee, load balancing/cell outage compensation).